Can an Interface have an inner class ?

Yes !

Example

public interface Abc {

  static int i=0;

  void dd();

  // class starts

  class a1 {

    a1()  {

      int j;

      System.out.println("inside");

    }

    public static void main(String a1[ ])  {

      System.out.println("in interfia");

     }

  }

}